The invention relates to a thermally and hydrothermally stable synthetic material having a high void volume attributable to tortuous mesopore-sized channels having a mean diameter between about 15 .ANG. and about 100 .ANG. and a narrow size distribution of less than or equal to about 30 .ANG., and a process for preparing same, so as to provide an excellent starting material for incorporation of active materials and the like.
Amorphous silica-aluminas are commercially used catalysts in many processes due to their acidity. The two most common methods for preparing amorphous silica-alumina are the controlled deposition of an alumina salt on a silica surface, and the co-precipitation of silica and alumina species from solution. In the first method, the silica surface is prepared from a silica gel, and alumina salt is hydrolyzed and precipitated by addition of aqueous ammonia.
The first method, controlled deposition of alumina on silica gel, leads to the generation of tetrahedrally coordinated aluminum, due to the controlled incorporation of the hydrolyzed aluminum atoms into the silica structure. In practice, however, this method is not desirable because the porosity of the silica gel collapses upon thermal treatment, for example during calcination, thereby making the aluminum atoms inaccessible to hydrocarbon molecules or other materials to be treated, thereby diminishing the practical value of such composition for commercial processes.
The second method, co-precipitation, leads undesirably to a large amount of octahedrally coordinated aluminum.
It is therefore evident that the need remains for a synthetic material wherein alumina and other active materials can be incorporated or deposited in tetrahedrally coordinated position with silica and wherein the composition maintains its porous structure without collapsing during calcination and/or other high temperature processes.
It is therefore the primary object of the present invention to provide a material on which active materials can be deposited and dispersed which material is thermally and hydrothermally stable.
It is a further object of the present invention to provide a method for preparing such a material.
Other objects and advantages of the present invention will appear hereinbelow.